The invention relates to a process for producing a molded insulating part, a molded insulating part produced by this process and a casting tool for producing a molded insulating part using the process.
Molded insulating parts which are joined with an accurate fit to a counterpiece to be insulated are known in various embodiments and are already in use. Thus, for example, the use of such molded insulating parts for insulating individual elements in the engine compartment or the exhaust gas train in motor vehicles is gaining increasing importance. The catalysts used in a motor vehicle, in particular, have to be brought to their operating temperature in a very short time and operated at this, which requires correspondingly complicated insulation. For this use, it is necessary to have, for example, a molded insulating part which can withstand temperatures of from 600° C. to above 1000° C. and can be optimally fitted between the surface of the catalyst and the outer wall thereof. The outer wall of the catalyst serving for thermal and acoustic shielding is generally made of a perforated metal sheet which has a complex shape and into which cut-to-size glass fiber mats are laid. Considerable amounts of scrap are naturally obtained here, and these are to be disposed of in a complicated manner. The glass fiber mat scraps are generally reused. In addition, the production of such insulation is associated with a considerable outlay in terms of work, which ultimately also increases the production costs. A further disadvantage is that the glass fiber mats cannot be optimally matched to the complex geometries of the wall of the catalyst and, for example, undesirable folding is required as a result, which can ultimately lead to premature wear of the molded insulating part and locally restricted insulation of the catalyst.
Apart from the use of the abovementioned glass fiber mats for producing insulation, producing molded insulating parts from an aqueous solution with fiber components introduced therein is also known. The mixture of fiber components and water with use of various additives is also referred to as “pulp”. Such production processes for a molded insulating part are known, for example, from DD 292 230 A5, with the pulp here in each case having proportions of organic compounds. A disadvantage of the organic constituents in the pulp is that these constituents lead on heating to damaging or at least troublesome or undesirable emissions, which is, in particular, of considerable importance in the abovementioned use of such molded insulating parts for insulating individual elements in the engine compartment or the exhaust gas train in motor vehicles.
WO 2011/018457 A1 additionally discloses a process for producing a dimensionally stable but not brittle molded insulating part from a fibrous insulating material, in which a textile sheet containing glass fibers and/or silicate fibers is treated with at least one silazane in solution or as solid, which can, for example, be effected by impregnation. The textile sheet can be a nonwoven, a knitted fabric or a woven fabric. For the present purposes, a silazane is a monomeric, oligomeric or polymeric silazane. To cure the silazane, it is additionally necessary to use a catalyst, with the document disclosing, for example, N-heterocyclic compounds, monoalkylamines, dialkylamines, trialkylamines, organic acids and similar organic substances or compounds. Some of these organic additives likewise have the abovementioned disadvantages. In addition, for example, the handling of organic solvents is difficult because of the health risks associated therewith and their combustibility. Additional production costs also arise because an after-combustion is usually necessary to remove the organic constituents.
DE 38 88 279 T2 relates to a process for producing a ceramic lining, wherein a ceramic slurry is introduced into a water-absorbing or water-withdrawing mold, where the mold has at least one water-impermeable seal in a region which after manufacture of the lining forms a valve hole. Absorption or uptake of water from the ceramic slurry results in deposition of the ceramic raw material present in the ceramic slurry. However, the peripheral edges of the lining produced in this way have to be corrected subsequently.
Furthermore, EP 1 081 285 A1 discloses a process for an article produced from a pulp, in which a pulp slurry which has a specific composition and is defined in more detail in the document is introduced into the hollow space of a mold and a preferably liquid flow medium is additionally used in order to press the pulp deposition body onto the interior wall of the hollow space of the mold. The process can be employed again using a pulp having a different composition, so that a multilayer body is formed thereby.
Finally, EP 1 927 447 A2 discloses monolithic, ceramic molded castings and pressure castings for chimney construction and corresponding processes for the production thereof. Here, a siliceous suspension is introduced by casting or by means of pressure casting into a casting mold having a porous surface, so that a green body is formed and after production is separated from the casting mold, dried and subsequently fired in a furnace.